A.Jackson De Havilland Aircraft since 1909 (Putnam)

De Havilland D.H.15 Gazelle

Although built purely for experimental purposes, the D.H.15 was allotted the type name Gazelle, a name which, like those of its predecessors, was little used. The aircraft was basically a D.H.9A, modified as a flying test bed for the 500 h.p. B.H.P. Atlantic twelve cylinder Vee watercooled engine, built by the Galloway Engineering Co. Ltd., and consisting of two 230 h.p. B.H.P. engines united on a common crankcase. Its installation in the D.H.15 called for a large frontal radiator similar to that used with the Liberty 12 engine, long exhaust pipes and vertical instead of raked front centre section struts as on the D.H.14. Standard D.H.9A armament was retained and comprised a synchronised forward firing Vickers gun on the port side and a Lewis gun on a Scarff ring on the rear cockpit. Two D.H.15s were ordered, only one of which was completed. This was actually J1937, the second aircraft, which in 1919-20 completed extensive flight testing of the Atlantic engine, piloted by Gerald Gathergood.

F.Manson British Bomber Since 1914 (Putnam)

Airco D.H.15 Gazelle

Although intended from the outset as an experimental test bed for the big Galloway Atlantic engine, the Airco D.H.15 (named the Gazelle, in line with the current practice of naming all military aeroplanes) was ordered by the Air Ministry on 7 September 1918. The single prototype, J1937, was a standard D.H.9A airframe with local structural modifications to accommodate the new engine, and retained all the standard D.H.9A’s armament, including provision to carry its bomb load - presumably so that a realistic performance comparison could be made with the standard aeroplane, as well as other variants. The Galloway Atlantic was evolved in much the same manner as the Siddeley Tiger, except that two standard cast-iron BHP cylinder blocks were brought together on a common crankcase. Drive to the two-blade propeller was without reduction gear, and a large rectangular frontal radiator, similar to that of the Liberty 12, was provided. Two other features readily distinguished the Gazelle. The long, almost horizontal exhaust pipe on each side of the fuselage extended as far aft as the gunner's cockpit, while the pair of front centre-section wing struts were rigged almost vertically, whereas previously they had been raked forward. J1937 was completed in July 1919, and was eventually delivered to Martlesham Heath for performance trials the following May. Compared with the standard Liberty-powered D.H.9A’s maximum speed of about 114 mph at 10,000 feet (without bomb load), the Gazelle achieved 133 mph under the same load conditions; it also displayed a 10 per cent all-round performance superiority over the 450hp Napier Lion-powered version of the D.H.9A.